1. Field of the Invention
The present invention relates generally to high performance GaAs and AlGaAs-based devices useful, in particular, as VLSICs, which devices possess a high degree of vertical and lateral electrical insulation between densely packed active devices and, more particularly, to a GaAs, AlGaAs device whose active region is surrounded by insulating stratums containing densely packed arsenic precipitates.
2. The Prior Art
The size of our federal budget and the size of what that budget buys in part do not always go in the same direction. For such is the case of electronic components required by our defense and space establishments as well as by our commercial enterprises. While the budgets balloon, electronic components continue to shrink in size to the micron and indeed to the sub-micron levels. In the field of electronics, miniaturization is the key.
The design and manufacture of integrated circuits (ICs) have long passed from medium to large-scale and to the very large scale size. Today's very-large-scale integrated circuits (VLSICs) pack densely their more than 20,000 logic gates or more than 64,000 bits of memory integrated with a single semiconductor substrate or deposited on the substrate by a continuous series of compatible processes. We are thus down to the micron and submicron sizes as regards the individual active devices integrated on a single chip. In order for such multiple-function chip circuit to function properly, not only must they possess good thermal stability, but there must exist a high degree of electrical isolation between the closely packed active devices. In the absence of a high degree of electrical isolation between and among the densely packed active devices, pernicious cross-talk occurs between neighboring devices. Such cross-talk renders the particular chip circuit utterly useless for its intended use involving space and defense applications as well as commercial applications.
Consequently, for a proposed design and manufacture of such a VLSIC to be acceptable for its intended purposes, a high degree of electrical isolation must be achieved between the densely-packed neighboring active devices. A great number of microelectronic and optoelectronic chips today are made of gallium arsenide (GaAs) and other III-V compound materials. These materials are widely used, inter alia, in the design and manufacture of field effect transistors (FETs) and lasers.
In the design of large-scale integrated circuits (LSICs), containing about a thousand active devices separated by about 3 microns on a single chip, mesa etching had been used to achieve acceptable electrical isolation between the devices. The typical breakdown voltage achieved was about 5 V. For most commercial applications this is acceptable. For defense and space applications however, much higher breakdown voltages are required.
Recently, GaAs layers grown by molecular-beam epitaxy (MBE) at very low substrate temperatures have gained considerable interest as buffer layers for GaAs metal-semiconductor field effect transistors (MESFETs) due to their high resistivity and excellent device isolations. See F. W. Smith et al, "New MBE Buffer Used to Eliminate Backgating in GaAs MESFET'S," IEEE Electron Device Letters, Vol.9, No. 2, February 1988. Although the low temperature (LT) MBE process has materially improved the device performance of GaAs circuits, it is both complex and expensive. Furthermore, the achieved buffer layers produced by LT-MBE are not readily controllable and at times incompatible with existing GaAs technology. The achieved resistivity of such buffer layers produced by LT-MBE also approaches currently acceptable minimum levels and may well be below requirements yet to come.
Other researchers in the field have succeeded in creating high resistivity buffer layers in GaAs integrated circuits by proton bombardment. See Donald C. D'Avanzo, "Proton Isolation for GaAs Integrated Circuits," IEEE Transactions on Electron Devices, Vol. ED 29, No. 7, July 1982; and J. D. Speight et al., "The Isolation of GaAs microwave devices using proton bombardment," Inst. Phys. Conf., Ser. No. 33 a, 1977, Ch. 5.
In the proton bombardment, the crystallinity of the bombarded area is destroyed, producing a semi-insulating layer. The effect is temporary, however, since over time the proton bombarded layer recrystallizes, thereby nullifying the isolation effect.
Hence, there exists a need for a submicron compatible technology to fabricate GaAs based VLSICs with higher effective packing densities than currently possible.